Advances in plasma processing have provided for growth in the semiconductor industry. In today competitive market, a manufacturing company needs to be able to minimize waste and produce high quality semiconductor devices. During substrate processing, conditions of the chamber may impact substrate processing. A critical parameter that may affect the plasma processing of substrates is the flow of the radio frequency (RF) current.
To facilitate discussion, FIG. 1 shows a simple block diagram of a capacitively-coupled plasma processing system with a processing chamber 100. Consider the situation wherein, for example, a substrate 106 is being processed within processing chamber 100. To ignite the plasma for etching substrate 106, a gas may interact with an RF current. The current may flow from an RF supply 122 along a cable 124 through an RF match 120 into processing chamber 100 during substrate processing. The RF current may travel along a path 140 to couple with the gas reactant to create plasma within a confined chamber volume 110 for processing substrate 106, which is positioned above a bottom electrode 104.
In order to control plasma formation and to protect the processing chamber walls, a set of confinement rings 112 may be employed. Set of confinement rings 112 may be made of a conductive material such as silicon, polysilicon, silicon carbide, boron carbide, ceramic, aluminum, and the like. Usually, set of confinement rings 112 may be configured to surround the periphery of confined chamber volume 110 in which a plasma is to form. In addition to set of confinement rings 112, the periphery of confined chamber volume 110 may also be defined by upper electrode 102, bottom electrode 104, insulator rings 116 and 118, an edge ring 114 and a lower electrode support structure 128.
In order to exhaust the neutral gas species from the confinement region (confined chamber volume 110), set of confinement rings 112 may include a plurality of slots (such as slots 126a, 126b, and 126c). The neutral gas species may traverse from confined chamber volume 110 into an external region 132 (outside chamber volume) of processing chamber 100 before being pumped out of processing chamber 100 via a turbo pump 134.
Those skilled in the arts are aware that unconfined plasma may cause an unstable processing environment. Ideally, the plasma formed during substrate processing is formed within confined chamber volume 110. However, under certain conditions, plasma may be ignited outside of confined chamber volume 110. In an example, given a high pressurized environment, the neutral gas species (which are being exhausted from confined chamber volume 110 into external region 132 of processing chamber 100) may encounter an RF field/magnetic field. The existence of RF current in the outside chamber may cause the formation of unconfined plasma 150.
In a typical processing environment, the RF current flows from RF generator into confined chamber volume 110. Those skilled in the arts are aware that RF current flowing into processing chamber 100 usually tries to return to its RF source. In a typical prior art configuration, a RF return path 142 may include the RF return current flowing along the inside of set of confinement rings 112. At point 152, the RF return current may flow along the outside of confinement rings 112 to bridge with the inside wall surface of processing chamber 100. From the chamber wall, the RF return current may follow a set of straps 130 to lower electrode support structure 128. From the surface of lower electrode support structure 128, the RF return current may flow back to RF source 122 via RF match 120.
As can be seen from the foregoing, by following path 142, the RF current flows outside of confined chamber volume 110 on its way back to RF source 122. As a result, a magnetic field or a RF field may be generated in the outside chamber region. The existence of an RF field/magnetic field may cause unconfined plasma 150 to be formed in external region 132 of processing chamber 100.
Since RF return current tends to seek a low impedance path, a set of straps may be employed to provide a low impedance path, thereby creating a shorter RF return path than path 142 (that follows the chamber wall), as shown in FIG. 2. In an example, a set of straps 230 may be employed to couple a confinement ring 212 to a lower electrode support structure 228 within a processing chamber 200. Thus, when the RF return current (flowing along a path 242) flows along the bottom side of outer wall of confinement ring 212, the RF return current may encounter a set of straps 230. Since the set of straps 230 provide a lower impedance path than the outer surface of confinement ring 212, the RF return current may bridge to lower electrode support stricture 228 via set of straps 230. From lower electrode support structure 228, the RF return current may continue onward to a RF source 222 via a RF match 220.
As can be appreciated from the foregoing, the RF return current path 242 is significantly shorter than path 142 of FIG. 1. However, a magnetic field/RF field may be formed in a region 244 between set of straps 230 and confinement ring 212. As a result, plasma may be ignited outside of the confined chamber volume (within region 244) given the right condition (such as the existence of gas reactants, a sufficiently high pressure volume, and an RF field/magnetic field).
Accordingly, an arrangement for providing a short RF return path while preventing the ignition of unconfined plasma is desirable.